DCMTK

Mail von ME vom 2008-04-02
Bei IHE gibt es als Teil des Mammographie-Integrationsprofils eine relativ
detaillierte Liste von Anforderungen in Bezug auf die Fensterung. Neben der
Unterstützung der "VOI LUT Function" (Sigmoid) wird dabei insbesondere auch
gefordert, dass ein Viewer Bilder mit VOI LUT "nachfenstern" können muss -
die Veränderung von Window Center/Width wirkt dabei als Skalierung der LUT.
Es wird auch (knapp) erläutert, wie das funktioniert.
Das wäre doch etwas, was wir in DCMTK (dcmimage) auch gerne hätten, oder...?

We have tried to explain this in the IHE Radiology Technical
Framework Volume 2, when we were adding in the Mammo profile.

Specifically:

"4.16.4.2.2.1 Display of Digital X-Ray, Mammo and Intra-Oral Images

For the “For Presentation” variant of the Digital X-Ray Image,
the Digital Mammography Image, and the Digital Intra-oral
X-Ray Image, the Image Display or Imaging Document Consumer actor
shall have both the capability to apply all the transformations
specified by the VOI LUT Sequence (0028,3010) and the capability
to apply all the transformations specified by the Window Width
(0028,1051)/Window Center (0028,1050)/VOI LUT Function (0028,1056)
attributes in the DX Image Module as selected by the user from
the choices available (e.g., guided by Window Center/Width
Explanation (0028,1055) or LUT Explanation(0028,3003).

If VOI LUT Function (0028,1056) is absent, then Window Width
(0028,1051)/Window Center (0028,1050) shall be assumed to be
the parameters of a linear window operation. VOI LUT
Function (0028,1056) values of “SIGMOID” and “LINEAR” shall be
supported.

The Image Display or Imaging Document Consumer shall support
the application of LUT Data (0028,3006) in items of the VOI
LUT Sequence (0028,3010) regardless of the Value Representation
(i.e., the DICOM standard allows either OW or US Value Representation).

The Image Display or Imaging Document Consumer actor must also
support pixel rendering according to the Grayscale Standard
Display Function (GSDF) defined in DICOM 2007 PS 3.14, because
the output values of these images are always P-Values.

If the DICOM image is referenced by other DICOM composite objects,
such as Grayscale Softcopy Presentation States, it is optional
for the Image Display or Imaging Document Consumer to actually
retrieve and display/apply these objects."

and

"4.16.4.2.2.1.1.4 Image Contrast Adjustment

As described in 4.16.4.2.2.1 Display of Digital X-Ray, Mammography
and Intra-Oral Images, the Image Display shall provide the user with
the ability to select amongst the available window and VOI LUT
choices available in the image object.

Subsequent to the initial application of the chosen contrast
transformation, the Image Display actor shall allow the user to
adjust the contrast without reverting to a purely linear
transformation:

- If the chosen contrast transformation is a lookup table, then
the Image Display shall allow the input value of the lookup table to
be stretched and translated so as to give the affect of adjusting
contrast and brightness whilst applying the same general shape as
the curve encoded in the lookup table. To provide feedback to the
user, the “window width” can be reported as the adjusted range of
input values to the LUT, and the “window center” can be reported
as the center value of that range.

- If the chosen contrast transformation is a sigmoid shaped VOI
LUT Function parameterized by the window center and width, then
the Image Display shall allow the window center and width values
to be adjusted and a sigmoid function reapplied.

If a Pixel Padding Value (0028,0120) only is present in the image
then image contrast manipulations shall be not be applied to those
pixels with the value specified in Pixel Padding Value (0028,0120).

If both Pixel Padding Value (0028,0120) and Pixel Padding Range
Limit (0028,0121) are present in the image then image contrast
manipulations shall not be applied to those pixels with values
in the range between the values of Pixel Padding Value (0028,0120)
and Pixel Padding Range Limit (0028,0121), inclusive."